Yes, there is a bug/error in victron system SOC calculation.
It is very close to an offset that would be generated if the multi/quattro self consumption was not included in the SOC calculation.
For some strange reasons victron ‘experts’ here just say the multi/quattro charging shunt/meter is either crude, inaccurate or non-existent, when its clearly actually pretty good apart from this offset.
Graphs showing this and a brief description available here (scroll up for first post):